Roseann Sdoia is recovering from her injuries from the Boston Marathon bombing, supported by family, friends and thousands of financial donors, even members of her beloved Boston Red Sox who visited her in the hospital.

But the one person she's not in touch with is perhaps the most important supporter of all: the man who she says saved her life.

Watch the full story on "20/20: In an Instant" tonight at 10 ET.

"I remember the whole thing," Sdoia, 45, said in an interview with "20/20" correspondent Deborah Roberts.

She was speaking of the moment the second explosion took away her right leg, and the life of 8-year-old Martin Richard, who was standing a few feet away. "I looked down and I saw a pool of blood," she said. "I knew that it was bad."

Sdoia, a resident of Dracut, Mass., not far from Boston, was in the midst of her annual routine April 15 when her life changed in an instant. Just as she had for the past 15 years, after cheering on the Red Sox at Fenway Park, she walked to her usual spot near the Boston Marathon finish line to watch the race.

Those around her began to panic after the first explosion down Boylston Street. Twelve seconds later, the second bomb exploded 2 feet away from her and five friends. In the aftermath, an anonymous stranger rushed in to help her.

"[A man] picked me up and dragged me to the middle of the street," she said. "And he took his belt off and did a tourniquet on my leg. I told him I couldn't get up, I couldn't get out of there because, 'I don't have a leg, I don't have a leg.' I don't know who he is. We've been looking for him."

Sdoia described him as a dark-haired man in his mid-20s, wearing a dark or navy-blue long-sleeved shirt, blue jeans and a brown belt.

Sdoia believes she would have died had it not been for the quick work of her "guardian angel." She was then put in the back of a "paddy wagon" and taken to the emergency room.

When asked whether she felt like giving up after realizing she'd lost a leg, Sdoia said, "Truthfully? Yes. I didn't want to live like this."

"Because of my family and my friends, I had to be here. I have to move forward. There's no looking back."

Those family and friends have rallied to help the woman they say is always there for her friends.

"Probably close to 50 people have already come to visit her," sister Gia Buckley said. "I don't think the ICU has ever seen so many people come through. She had friends fly in from Florida and Arizona. We've had to hold people off and create a schedule because we don't want it to be overwhelming, but everyone has understood."

One close friend, Christine Rousseau Hart, set up an online fundraiser soon after the bombing to help Sdoia with "all expenses incurred due to this tragic event."

Hundreds of thousands of dollars have already been raised for Sdoia and the funds continue to climb with each hour ($291,692 from 3,902 people in nine days).

"This is a great way for me to help her, because who knows what the financial burden will be from this," Hart said. "It's amazing, the amount of people that are reaching out and donate. From $5 to $500, people have even donated up to $2,500. It's overwhelming the goodness of people, whether they know Roseann or not."

Sdoia was also able to connect with Bree McMahon, 21, who lost her right leg in a 2009 accident at a car wash fundraiser in which a car pinned her legs against a wall. She has since gone on to play Division II soccer for Brevard College in Brevard, N.C.

"It's tough and it's going to kind of suck," McMahon told Sdoia. "[But] I can tell you're tough so I'm sure you'll be great through it."

Offering words of support and advice on possible prosthetics, McMahon said she hopes to be a friend to those like Sdoia facing a new reality.

"It puts a smile on someone's face to see, 'Wow she's dealing with something that I'm going through right now,'" McMahon said. "It's not over. You may not be able to do the things you used to do, the exact same way. But there are still things you can do."

Sdoia too finds comfort in meeting McMahon and other amputees.

"I'm taking all of this information into my head and hoping that moving forward, knowing what they have done, will propel me to do what I want to do," Sdoia said. "When there's a tragedy like this, it does nothing but bring people together."

Watch Roseann Sdoia and Bree McMahon's story on "20/20: In an Instant" tonight at 10 ET.